MP4603 White LED Driver for Large LCD TV Backlights

Transcription

1 The Future of Analog IC Technology MP4603 White LED Driver for Large LCD TV Backlights DESCRIPTION The MP4603 is an integrated white LED driver. It uses MPS s patent-pending technology to drive the backlights for LCD TVs measuring 60- inches or larger, for LED string voltages up to 350V. This novel technology can leverage the LED drive power by regulating only a small portion of the LED drive voltage together with a fixed high-voltage source, a low-voltage LED driver can drive high voltage LED strings. This method allows for a super-high power density, higher efficiency and lower cost due to the low voltage stress, higher switching frequencies, and smaller passive components. The MP4603 is a current-mode controlled buck-boost regulator. With a 12V input V INL and a high voltage source V INH, it can deliver a regulated voltage (V INH to V INH +68V) to drive a LED string with up to 100 LEDs. It can drive an external switch in series with the LED string to achieve over 1:1000 dimming ratio. Analog dimming can be applied at the same time to further improve the dimming ratio. Fault protections include LED open-string protection, output short-circuit protection, cycle-by-cycle peak current limiting, and thermal shutdown. The MP4603 is available in SOIC16 package. FEATURES Novel Power-Leverage-Control Technology Unique Step-Up/Down Operation Up to 99.5% Efficiency 0.5Ω Internal Power MOSFET Switching Frequency Synchronization Over 1:1000 Dimming Ratio Separate Analog and PWM Dimming ±5% 200mV Reference Voltage 10μA Shutdown Mode Cycle-by-Cycle Over-Current Protection Thermal Shutdown Protection LED String Open and Short Protection FAULT Output at LED Protection Output Short-Circuit Protection Available in SOIC16 Package APPLICATIONS Large LCD Panels Backlighting High Power Street LED Lighting All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under Products, Quality Assurance page. MPS and The Future of Analog IC Technology are registered trademarks of Monolithic Power Systems, Inc. MP4603 Rev

2 TYPICAL APPLICATION V INH MP4603 Fault R FAULT 100K FAULT BST SW C BST 100n L1 C IN INGND VSS R1 CLK/SYN SYN DGD PWM PWM OVP C OUT EN EN FB R FB ADIM ADIM COMP R FST 300K FST SLOPE R SLOPE 300K C COMP 10n R2 MP4603 Rev

3 ORDERING INFORMATION Part Number Package Top Marking Free Air Temperature (T A ) MP4603ES* SOIC16 MP4603ES -20 C to +85 C * For Tape & Reel, add suffix Z (e.g. MP4603ES Z); For RoHS Compliant Packaging, add suffix LF (e.g. MP4603ES LF Z) PACKAGE REFERENCE PIN 1 ID TOP VIEW FAULT 1 16 BST 2 15 SW INGND 3 14 VSS SYN 4 13 DGD PWM 5 12 OVP EN 6 11 FB ADIM 7 10 COMP FST 8 9 SLOPE SOIC16 ABSOLUTE MAXIMUM RATINGS (1) V V SS V to 85V V INGND V SS V to 85V V SW V SS V to V IN + 0.3V V BST... V SW + 6V V DGD V SS V to +12V V V OCP V to +6V V OVP, V FB, V COM, V FST V SS V to +6V V ADIM, V EN, V PWM, V SYN V INGND V to +6V Continuous Power Dissipation (T A = +25 C) (2) SOIC W Junction Temperature C Lead Temperature C Storage Temperature C to +150 C Recommended Operating Conditions (3) Supply Voltage V V SS...5V to 80V V ADIM, V EN, V PWM, V SYN V INGND...0V to 5V Maximum Junction Temp. (T J ) C Thermal Resistance (4) θ JA θ JC SOIC C/W Notes: 1) Exceeding these ratings may damage the device. 2) The maximum allowable power dissipation is a function of the maximum junction temperature T J (MAX), the junction-toambient thermal resistance θ JA, and the ambient temperature T A. The maximum allowable continuous power dissipation at any ambient temperature is calculated by P D (MAX) = (T J (MAX)-T A )/θ JA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 3) The device function is not guaranteed outside of the recommended operating conditions. 4) Measured on JESD5 1-7, 4-layer PCB. MP4603 Rev

4 ELECTRICAL CHARACTERISTICS V = 12V, PWM and AD Pins floating, R FST =51kΩ, T A = +25 C, V VSS =V INGND =0V, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units FB Feedback Voltage V FB mv FB Input Current I FB V FB = 0.2V μa UVLO Rising V TH V UVLO Hysteresis V HYS 400 mv Shut Down Current I off V EN =0V 10 μa Supply Current (Quiescent) I Q V PWM = 0V, V FB = 250mV ma Switch-On Resistance (5) R DS(ON) 0.5 Ω V Switch Leakage I =80V, V EN =0V, SWLK 1 μa V PWM =0V, V SW =0V Switch Current Limit (5) I S_MAX 2.5 A FST pin open MHz Oscillator Frequency f SW RFST = 200kΩ khz FST Output Voltage V FST V Fold-back Frequency f SWFB V FB = V OVP = 0V, FST pin open 160 VFB = V OVP = 0V, R FST = 200kΩ 40 Slope Compensation S SLOPE SLOPE pin open RSLOPE = 200kΩ SLOPE Pin Output Voltage V SLOPE V Maximum Duty Cycle D MAX V FB = 0.15V,FST pin open 88 % Minimum ON-Time (5) t ON 270 ns V SYN = 3.3V 400 SYN Input Current I SYN VSYN = 0V -750 Frequency Synchronization Range (5) f SW_SYN MHz PWM Dimming OFF Threshold V PWML V PWM Falling 1.65 V PWM Dimming ON Threshold V PWMH V PWM Rising 2.2 V PWM Dimming Frequency k Hz Minimum Analog Dimming Threshold V ADMIN V FB = 5mV 0 mv Maximum Analog Dimming Threshold V ADMAX V FB = 200mV 1.2 V ADIM Input Current V ADIM = 3.3V 36 V ADIM = 0V -3.5 EN OFF Threshold V ENL V EN Falling 0.9 V EN ON Threshold V ENH V EN Rising 1.5 V EN Input Current I EN V EN = 3.3V 3.8 μa khz V/μs μa μa MP4603 Rev

5 ELECTRICAL CHARACTERISTICS (continued) V = 12V, PWM and AD Pins floating, R FST =51kΩ, T A = +25 C, V VSS =V INGND =0V, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units V Dim Gate Driver Sourcing Current I DGD V SS = 0V, DGD+ -25 ma V PWM =3V V Dim Gate Driver Sinking Current I DGD V SS =10V, DGD- 45 ma V PWM =1.5V LED Open OV Threshold V OVPTH 1.2 V LED Short Threshold for Immediate Latch-Off V FBS 600 mv LED Short Delay for Latch-Off τ D_FBS 300mV < V FBS < 600mV 450 μs Thermal Shutdown (5) 150 C Thermal Shutdown Hysteresis (5) 20 C Note: 5) Guaranteed by design. MP4603 Rev

6 TYPICAL CHARACTERISTICS MP4603 Rev

7 TYPICAL PERFORMANCE CHARACTERISTICS Performance waveforms are tested on the evaluation board of the Design Example section. V IN = 12V, V INH = 125V, V LED =180V I LED = 120mA, T A = 25 C, unless otherwise noted. PWM Dimming Curve Analog Dimming Curve Steady State V SW LED CURRENT (ma) LED CURRENT (ma) V IN 10V/div. V SS 20 I L 0 500mA/div V ADIM_EVB (V) Start EN Start PWM Dimming f PWM =200Hz, D PWM =50% V SW V SW V SW V IN 10V/div. V SS V EN 5V/div. V SS V PWM 5V/div. V SS I LED 100mA/div. I LED 100mA/div. I LED 100mA/div. Open LED Working Short LED- to Working V SW V SW V FAULT 5V/div. V SS V FAULT 5V/div. V SS I L 500mA/div. I SHORT 5A/div. MP4603 Rev

8 PIN FUNCTIONS Pin # SOIC16 Name Description 1 FAULT Fault Condition Output. Open drain with reference to INGND. FAULT is high-z during normal operation, and pulled to INGND when LED short protection or LED open protection trigger. 2 Positive Voltage Input. Requires a decoupling capacitor to prevent large input-voltage spikes. 3 INGND Input Ground Reference. 4 SYN Frequency Synchronization Input. The switching frequency can be synchronized with an external clock. Multiple ICs frequencies can also be synchronized without the external clock by connecting all the SYN pins together. They follow the highest set frequency. 5 PWM PWM Dimming Input. Apply a 100Hz to 50kHz square wave signal with amplitude greater than 2.2V. The PWM pin voltage is high if left floating. 6 EN Enable Input Pin. A voltage greater than 1.5V will turn on the chip. 7 ADIM Analog Dimming Input. A voltage in range of 0V to 1.2V on ADIM pin adjusts the LED current from 0 to 100%. The ADIM pin voltage is high (about 3.3V) if left floating. 8 FST Frequency Set. A resistor from FST to VSS sets the switching frequency if there is no SYN input. If left open, switching frequency reverts to an internal default value. 9 SLOPE Programmable Slope Compensation. Connect a resistor from SLOPE to VSS to set the slope-compensation peak amplitude. If left open, slope compensation reverts to an internal default value. 10 COMP Error Amplifier Output. Connect a capacitor 1nF from the COMP pin to VSS to improve the stability and to provide a soft-start on start-up or for PWM dimming. 11 FB LED Current Feedback. The MP4603 regulates the voltage across the current sensing resistor between FB and VSS with 200mV. If the FB voltage exceeds 300mV for 450µs or exceeds 600mV, LED short protection triggers. 12 OVP Over Voltage Protection. Use one external resistor voltage divider from the output to VSS to program the OVP threshold. This voltage references VSS. When the OVP pin voltage reaches the 1.2V threshold, the switch turns off and the IC latches off. When the OVP pin voltage falls below 0.4V and the FB pin voltage is less than 0.1V, the chip frequency folds back. Program the OVP pin voltage from 0.4V to 1.2V for normal operation. 13 DGD LED Dimming-Switch Gate Drive Output. 14 VSS Negative Voltage Output. The voltage reference for OVP, FB, COMP, SLOPE, DGD and FST. 15 SW Switch Output. The source of the internal MOSFET switch. Connect to the power inductor and cathode of the Schottky rectifier. 16 BST Bootstrap. Connect a capacitor between the SW and BST pins to form a floating supply across the power switch driver. MP4603 Rev

9 BLOCK DIAGRAM SYN SYN 20X EN DDIM ADIM INGND EN DDIM Dimming ADIM Control INGND ENI VBG Bandgap & Bias EN VBG INGND INGND OSC VBG SC FST CLK VBG VBG BST BST Regulator HSG DR BST FBREF V0P20 V0P20 DIMIN VSS V0P20 SCST Current Limit ILIM SW VSS VSS Over- Voltage Protection OV OVP VSS SW OVP FST SLOPE FB REF FB DIMIN Soft- Start EA Control Loop PWM COMP OV CLK FALTDRV Logic ILIM PWM HSON Level Shift VSS INGND Diming FET Gate Drive DIMIN FAULT DGD COMP VSS Figure 1: Functional Block Diagram MP4603 Rev

10 OPERATION The MP4603 is a current mode regulator. The sensing resistor senses the LED current and the signal goes an error amplifier, which regulates it to 200mV through an internal compensation network The COMP pin is the output of the error amplifier. The inductor peak current is proportional to the COMP voltage. Increasing the COMP voltage increases the current delivered to the output. LED Open Protection If the LED is open, there is no voltage on the FB pin. The duty cycle increases until V OVP -V VSS reaches the shutdown threshold. The top switch turns off, and the IC latches off. At LED open protection, the Fault pin goes low. LED Short Protection If the FB voltage exceeds 600mV, the IC immediately latches off and DGD goes low. If the FB voltage exceeds 300mV for around 450µs, IC latches off and DGD goes low. The EN pin must reset to restart the IC. The Fault pin goes low when the IC latches off. Dimming Control The MP4603 allows for both Analog and PWM dimming. The analog dimming voltage range on ADIM goes from 0V to1.2v to change the LED current from 0% to 100% of the maximum LED current. If the voltage on the ADIM pin exceeds 1.2V or is floating, LED current goes to its maximum. PWM dimming uses a square-wave signal with a 100Hz-to-50kHz frequency range and an amplitude over 2.2V applied to the PWM pin. PWM dimming can achieve over 1:1000 dimming ratio with PWM frequency less than 200Hz During the PWM dimming OFF interval, an internal switch disconnects the COMP pin capacitor from the output of the error amplifier: This holds the COMP voltage during the PWM OFF interval and increases the LED current response speed to achieve a high dimming ratio. Combine PWM and analog dimming to increase the dimming ratio. Apply a 100Hz to 50kHz PWM signal on PWM pin and a analog dimming signal in range of 0V to 1.2V on ADIM pin.. MP4603 Rev

11 APPLICATION INFORMATION The MP4603 is a buck-boost LED driver. Its novel power leverage control technology provides a highly efficient, low-cost solution for LCD TV LED drivers. It has a high bus voltage and a low supply voltage (typically 12V or 24V, up to 60V) to drive LED backlight strings of >350V for LCD TVs measuring 60-inch or more. Setting the LED Current An external resistor (R FB ) sets the maximum LED current as per: 0.200V RFB = I Setting the Switching Frequency An external resistor R FST can set the switching frequency (f S ) as per: 60k fs = 0.95MHz R This equation applies to a programmable frequency range between 200kHz and 2MHz. If FST pin is floating or R FST exceeds 400kΩ, the switching frequency is set to default value of 0.9MHz. Setting the Slope Compensation The MP4603 employs peak-current mode control, which needs slope compensation to avoid sub-harmonic oscillation when the duty cycle exceeds 50%. The current loop has effective sense resistance of 0.4Ω. Given a desired input/output voltage relationship, estimate the sense current rampdown slope as: S V L LED FST L DOWN = μ 0.4V/ s Where V L is the voltage across the inductor in volt; and L is the inductor value in μh. Ensuring current loop stability requires a compensation slope of at least half of the rampdown slope: S SC 1 >= S 2 DOWN An external resistor (R SLOPE ) can set the slope compensation for the current loop as per: 60k S V SC =0.6 * μs R SLOPE The equation is effective only for a resistor range from 20kΩ to 400kΩ for R SLOPE. If SLOPE pin is floating or R SLOPE exceeds 400kΩ, the slope compensation is set to default value of 0.5V/μs. Selecting the Inductor The input voltage, output voltage, and LED current factor into inductor selection. In addition, select the inductor so that the circuit always operates in continuous current mode (CCM). Estimate the inductor value using the following equation: VOUT L = f (V + V ) ΔI S IN OUT L Where ΔI L is the inductor peak-to-peak current ripple. Design ΔI L somewhere around 40% to 60% of the inductor average current, which is: V = +. OUT IL _ AVG I LED (1 ) Select an inductor that does not saturate at the maximum peak current, which is: IL_PK = IL_AVG Δ IL. Selecting the Input Capacitor The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. Use ceramic capacitors with X5R or X7R dielectrics because they have low ESR values and small temperature coefficients. Select a sufficiently-large capacitance to limit the input voltage ripple (ΔV IN ), which is normally less than 5%-10% of the DC value. C IN IL_AVG VOUT > f ΔV (V + V ) s IN IN OUT MP4603 Rev

12 Selecting the Output Capacitor The output capacitor normally limits the output voltage ripple (ΔV OUT ) to less than 1%-to-5% of the DC value, and ensures a stable feedback loop. Select an output capacitor value with low impedance at the switching frequency. Use ceramic capacitors with X5R or X7R dielectrics for their low ESR characteristics. C OUT ILED VOUT > f ΔV (V + V ) s OUT IN OUT Setting the Over Voltage Protection The output voltages of some converters, such as buck-boost and boost converters, can rise to very high levels without a limiting function. Overvoltage protection (OVP) limits the output voltage to below the operating rating. Use a voltage divider to set the OVP point. R V = + 1 OVP 1.2V (1 ) R Where R 1 and R 2 are the voltage divider (refer the TYPICAL APPLICATION). For most applications, set the OVP point around 10% to 30% higher than the output voltage. Check that the set OVP point will not exceed the operation rating. FAULT Condition Output The MP4603 has an open drain output as a FAULT indicator. Under normal conditions, FAULT is a high-z output and can be set to any desired voltage with external resistors. However, if V FB exceeds VSS by 600mV, or V FB exceeds VSS by 300mV for ~450μs, or OVP triggers at 1.2V, FAULT drops to the INGND level. The R dson for this pull down switch is ~100Ω. PC Board Layout Place the high-current paths (VSS, and SW) very close to the device with short, direct, and wide traces. Place the input capacitor as close as possible to the and VSS pins. Place the external feedback resistors next to the FB pin. Keep the switch node traces short and far away from the feedback network. Pay attention to the layout of the high frequency switching loop, which should be placed as small as possible. 2 For buck applications, the high frequency switching loop is composed of the input capacitor, the internal switch of IC ( pin to SW pin) and the diode. Place the input capacitor and the diode close to the IC. For buck-boost applications, the high frequency switching loop is composed of the input capacitor, the internal switch, the diode and the output capacitor. Place the input and output capacitors close together, close to the IC, and to the diode. Top Layer Bottom Layer Figure 2: PCB Layout MP4603 Rev

13 MP4603 WHITE LED DRIVER FOR LARGE SIZE BACKLIGHTING TYPICAL APPLICATION CIRCUITS 150V V INH LED+ 12V VLED 180V MP4603 Block1 Fault 12V R FAULT 100K C IN FAULT INGND BST SW VSS C BST 100n L1 R1 Fault CLK/ SYN PWM EN ADIM R FST 300K SYN PWM EN ADIM FST DGD OVP FB COMP SLOPE R SLOPE 300K C COMP 10n R2 R FB C OUT 12V CLK/ SYN PWM EN ADIM Block2 LED- LED- Figure 3: White LED Driver for TV Applications MP4603 Rev

14 MP4603 WHITE LED DRIVER FOR LARGE SIZE BACKLIGHTING Design Example This design example shows an LCD TV LED backlight application. Figure 4 shows the system power structure block diagram. MPS s HFC0100 flyback controller controls the flyback, offering 2 outputs: 12V IN and V INH. The high output, V INH, provides a bias voltage (less than the LED string voltage) for all LED strings and connects to the anodes. The low output, 12V IN, is about 12V and supplies the MP4603 LED driver; the MP4603 generates a negative voltage and connects to the cathode of the LED strings to drive the LED strings. V INH AC Input HFC0100 Flyback 12V IN MP4603 LED Driver INGND MP4603 LED Driver INGND LED1- LED2- Figure 4: System Power Block Diagram Specifications Protections: Flyback Output: Open LED string protection V INH = typical 145V (140V to 160V): crossregulation in the multiple output flyback is the Short LED string protection MP4603 Operating Range: primary cause of the large tolerance. Input voltage = 12V 12V IN is 12V; Output voltage = -5V to -55V Output: LED current = 120mA. 2 outputs of 120mA for every string Figure 5 shows the schematic of the MP4603 LED voltage is typical 180V (165V to 195V) LED driver stage. JP1 is short and JP2 is open. Switching frequency: ~200kHz MP4603 Rev

15 MP4603 WHITE LED DRIVER FOR LARGE SIZE BACKLIGHTING Figure 5: LED Driver Schematic Used for Evaluation (EV4603-S-00A) Setting Current Sense Resistor The sense resistor R FB is: R FB 0.200V = I Use two 3.32Ω resistor in parallel (R15 and R16) as the LED current sensor resistor. Setting the Frequency Set Resistor The following equation determines the frequency set resistor, R18: LED 0.95MHz 60k R18 = f Select 300kΩ to set the switching frequency to about 200kHz. Selecting the Inductor Select an inductor such that the circuit always operates in CCM as per the following equation: _min VOUT_max L1= VOUT_max f S (_min + V OUT_max ) η I LED(1 + ) V S IN_min Where η is about 40% to 60%. Select an inductance of 100μH and the inductor peak-topeak current of 0.49A. Select an inductor that does not saturate at the maximum peak current, which is: IL_PK = IL_AVG Δ IL Select L1=100μH with a saturation current of 1.5A Setting the Slope Compensation The voltage across the inductor in the buckboost converter is the output voltage. The maximum slope compensation is: VOUT_max SDOWN = 0.4V/ μs L To ensure current-loop stability, select a compensation slope that is at least half of the needed ramp-down slope: S SC 1 >= S 2 DOWN S SC 0.11V/μs. Use the slope compensation resistor R SLOPE to set the slope compensation for the current loop as per the following equation: 0.6 V μs R19 = 60kΩ S Based on this equation, the slope compensation resistor cannot exceed 330kΩ. SC MP4603 Rev

16 MP4603 WHITE LED DRIVER FOR LARGE SIZE BACKLIGHTING Select R19=300kΩ as the compensation resistor. Selecting the Input and Output Capacitor Estimate the input capacitor and output capacitor using the following equations. C C IN OUT IL_AVG VOUT > f ΔV (V + V ) s IN IN OUT ILED VOUT > f ΔV (V + V ) s OUT IN OUT Where ΔV IN is about 5%-to-10% of the input voltage, and ΔV out is about 1%-to-5% of the output voltage. Select C2=2.2μF ceramic capacitor as the input capacitor and C8=2.2μF as the output capacitor Setting the Over Voltage Protection Set the OVP point is about 1.1x-to-1.2x of the output voltage so that the OVP point is about 60V to 66V. R5 VOVP = 1.2V (1 + ) R Select R12=20kΩ and R5=1MΩ; the OVP point is 63V. 12 MP4603 Rev

17 MP4603 WHITE LED DRIVER FOR LARGE SIZE BACKLIGHTING PACKAGE INFORMATION SOIC ( 9.80) 0.394(10.00) 0.024(0.61) 0.050(1.27) (1.60) PIN 1 ID (3.80) (4.00) (5.80) (6.20) (5.40) 1 8 TOP VIEW RECOMMENDED LAND PATTERN 0.013(0.33) 0.020(0.51) 0.050(1.27) BSC 0.053(1.35) 0.069(1.75) SEATING PLANE 0.004(0.10) 0.010(0.25) SEE DETAIL "A" (0.19) (0.25) FRONT VIEW SIDE VIEW GAUGE PLANE 0.010(0.25) BSC 0 o -8 o 0.016(0.41) 0.050(1.27) DETAIL "A" 0.010(0.25) 0.020(0.50) x 45o NOTE: 1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS. 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. 4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX. 5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION AC. 6) DRAWING IS NOT TO SCALE. NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP4603 Rev

18 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Monolithic Power Systems (MPS): MP4603ES-LF MP4603EF-LF-Z MP4603ES-LF-Z MP4603EF-LF